One way to test earplugs is to insert an earplug in an ear canal of a person, or of a manikin head with an ear simulator that simulates the acoustic characteristics of the ear and that has a sound detector. Then sound of a controlled amplitude is applied to the person or manikin. The amplitude of sound detected by the person or ear simulator is noted in relation to the amplitude of sound applied to the outside of the ear canal, to indicate the effectiveness of the earplug. When a person who is going to wear an earplug wishes to test it, it is desirable that that person test it on him/herself.
One problem encountered when applying sound through an earphone, or headphone, is that the amplitude of sound applied to the outside of the ear may not be sufficiently high over the frequency range of interest. One test used in the industry measures the blocking ability of earplugs at five frequencies: 250 Hz, 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz. It would be desirable if the amplitude of sound output from the headphone were approximately the same at each of these frequencies for a constant electrical power input. It also would be desirable if the headphone were as efficient as possible. Although low speaker output can be compensated for by a higher power input, the speaker output at higher amplitudes will be distorted, and an excessively high electrical input can damage the speaker.
Conventional headphones place the speaker so it lies close to the outer ear. During earplug effectiveness tests, the earplug can touch the headphone grille and prevent the headphone from fully seating on the ear, or disturb the earplug installation, or make the wearer uncomfortable.